Historically, people first wore shoes to protect their feet. Over the centuries, footwear evolved into many different types that were specific to particular activities. Thus, the protection offered by a cold-weather work boot is highly different from that offered by a running shoe. In addition to protecting the feet, athletic footwear has further developed to offer specific functions dependent on the particular sport. Soccer shoes, for instance, have spikes for traction; whereas cycling shoes have very stiff soles with mounting plates for cleats to engage the pedal. In this manner, golf shoes have evolved to provide the wearer with good traction on grass, comfort while walking, and a stable platform for hitting the ball. Typical golf shoes thus have a relatively stiff sole with metal spikes or plastic cleats.
A stiff sole, while providing a stable platform, can nonetheless cause discomfort because there is a balance between how the foot should be allowed to move versus how it should be supported. An example of this is the fact that during walking and at the start and finish of the golf swing, the foot bends at the metatarsal joints (the ball). Aside from the physical effort needed to flex a very stiff sole (which would tend to cause a ‘clunky’ gait as when wearing clogs), sole stiffness tends to cause the heel of the foot to slide up and down in the heel cup, potentially causing blisters. Thus, golf shoes have evolved to have soles that flex across the ball area to allow this movement without compromising the lateral stability of a good hitting platform.
Relatively recent studies in biomechanics have sought to better quantify how the 26 bones of the foot move relative to each other during human movements. One particular motion that has been identified is a torsional movement about the long axis of the foot. In effect, the forefoot and rearfoot twist relative to each other. It is thought that this movement smooths the contact between foot and ground, decreasing impacts with the ground as well as providing better ground contact. This observation has led to the development of a golf shoe sole to allow this natural movement.
U.S. Patent No. Re. 33,193, reissued from U.S. Pat. No. 4,608,970, to Marck et al. discloses an orthopedic device for correcting infants' feet. The device includes a posterior part, an anterior part, and a ball-and-socket for allowing three degrees of freedom between the posterior and anterior parts during set-up. These parts are immobilized in a particular position, when the device is in use. As a result, this device does not assist with the natural torsional-like action of the foot in walking where such action is missing.
U.S. Pat. No. 3,550,597 discloses a device that facilitates the natural rolling action of the foot during movement by providing a flat construction with front and rear main lifting sections rigidly connected to a resilient intermediate section that is twisted into the form of a flat torsion spring. The device applies a yieldable torsional action during use that is applied to the foot by the lifting sections, whereby the heel of the foot is urged upwardly at the inner side and the forefoot is raised upwardly at the outer side, producing a torsional action similar to the natural torsion action of the foot.
Another construction intended to provide greater support to the wearer of the shoe is disclosed in U.S. Pat. No. 5,243,776 to Zelinko. The Zelinko golf shoe has a sole having a forward end, a heel end and an intermediate portion joining the two ends. A spike support plate is journaled to a post extending from the forward end of the shoe. The spike support plate is so mounted to the forward end for rotation about a vertical axis. A biasing means, such as tension springs, is provided to connect the spike support plate to the heel end and for constantly biasing the spike support plate to a neutral (i.e., non-rotated) position and returning the support to that position after the support has been rotated. A cover is provided to protect the biasing means. The Zelinko golf shoe is constructed to allow the forward end of a golfer's foot to remain fixed during a golf swing while the heel rotates.
There remains a need for an improved outsole for a shoe that enables individual movements of the foot, particularly, the rotation between the rearfoot and the forefoot. By allowing and controlling these rotations, the outsole would resists torsional instability during play, provides independent traction suspension, and increases the flexibility of the shoe to accommodate the movement of the wearer.